Well at the first place, if you are using microsoft iis server, it should probably be for asp files probably! but if you are 
using it for php files, then there is pratically no point in using it! as there are far better and supported linux based servers presend, and even if you want to use microsoft windows based system to run your server, there are windows based packages available instead of iis which support php far better than iis and have many needed features by default like for example mod_rewrite , enabling usage of .htaccess files on the server for improving many thing including url structure of your site.
How ever, in any case if you still need to use the microsoft iis server for your files, and also need to use the .htaccess, there is no such alternative for iis server by default as far as i know! you have to install this module for iis server called mod_rewrite for iis server. This will enable the mod_rewrite facility for your microsoft iis based server running php files and you will be able to use the .htaccess easly. You can download the files from the following link along with all details and installation instructions:
http://www.iis.net/downloads/default.aspx?tabid=34&g=6&i=1470